to the highway tunnels, new york city thrives because of their work. ryan: you got one little hole in the ground, and nobody knows we're here. see the empire state building, right. that's 1,000 feet. so you figure, you go down 1,000. how high that is -- that's how far we go down. narrator: stretching more than 60 miles under the city, tunnel 3 is taking generations of workers to complete. ryan: i don't even want to imagine what my father had to go through. when we first started, it was a rough job. everything was dynamite. now, they have these machines called "moles." it's like a big drill, and it just cuts right through the ground. so there's no more dynamite. and it's still a rough job, but it's gotten to a point where it's a lot safer. in the '70s, we lost a man a mile basically. here, maybe we've had two or three deaths in the last 20 years, which is too much anyway, but it's cut down a lot. hurwitz: city tunnel number 3 will be an opportunity to take city tunnel 1 out of operation and rehabilitate it. city tunnel number 1 had one valve to shut off the whole tunnel. city tunnel 2 had two par